I am an evolutionary biologist interested in between-individual variation of life-history, morphological, and behavioural traits in natural populations. My main research objective is to understand the ecological and evolutionary mechanisms underlying variation in these characters, with a special focus on the role of environmental degradation. This degradation can be internal, (the decrease of individual fitness with age due to senescence); or external, (changes in the environment, including those induced by man). I conduct analyses based on long-term datasets collected in wild bird populations, presently mainly blue tits (Cyanistes caeruleus) and great tits (Parus major).